The present invention relates to molded antimicrobial articles, particularly antimicrobial fibers excellent in industrial washing durability, and a production process thereof.
Molded antimicrobial articles, especially fibers, are widely used for various clothes, interlinings, linings, bedclothes, interior products and the like. These fibrous products are excellent in antimicrobial activity and, by various improvements, have become good in household water washing durability.
However, in recent years, occurrences of infection in hospitals due to methicillin resistant Staphylococcus (MRSA) has become a problem. As a countermeasure, white overalls, covers, sheets, curtains and the like have been treated in an attempt to impart antimicrobial characteristics. However, these fibrous products for use in hospitals are usually very frequently industrially washed at 60 to 85xc2x0 C., and few conventional techniques provide sufficient durability against such washing.
Fibers have been treated to impart antimicrobial characteristics by blending an inorganic antimicrobial agent such as silver, copper or zinc into synthetic fibers at the spinning stage, or by applying an organic antimicrobial agent such as a quaternary ammonium salt by spraying or padding in a post-treatment. The former method is excellent in view of washing durability, but does not permit antimicrobial treatment at a later stage. Furthermore, the antimicrobial agent precipitates as crystals on the spinneret face during spinning to cause frequent fiber breaking and the like, which is a problem in the yarn production process. On the other hand, the latter method is poor in washing durability of antimicrobial activity, although it advantageously allows antimicrobial treatment in a later stage.
JP-A-61-239082 describes treating N6 socks in a pyridine based antimicrobial agent suspension at 130xc2x0 C. for 60 minutes with shaking. However, when a suspension is used, the particle size of the antimicrobial agent is too large to obtain a sufficient effect. Furthermore, JP-A-09-273073 describes treating polyester fibers with a pyridine based antimicrobial agent simultaneously with dyeing, but the antimicrobial agent used is not proper and does not provide a sufficient effect.
Accordingly, it is highly desirable to provide a molded antimicrobial fibrous product excellent in industrial washing durability and a production process thereof.
The present invention relates to a molded antimicrobial article, comprising an infiltrated antimicrobial agent which forms independent phases of 0.01 xcexcm or more in short diameter in the molded article. It is preferable that a pyridine based antimicrobial agent with a molecular weight of about 200 to about 700 and an inorganic property/organic property value of about 0.3 to about 1.4 forms independent phases of about 0.01 xcexcm or more in short diameter in the molded article, and that about 50% or more of the antimicrobial agent is infiltrated to a depth range of about 0.5, preferably, about 1 xcexcm or more from the surfaces of fibers, or about 30% or more of the antimicrobial agent is infiltrated to a depth range of about 2 xcexcm or more from the surfaces of fibers. It is also preferable that the molded articles are fibers, that the surface area used per 1 g of fibers is about 0.1 m2 or more, and that the synthetic fibers are a colored antimicrobial fibrous product.
The molded antimicrobial article of the invention can be obtained, for example, by immersing a fibrous product in a dyeing liquid containing a pyridine based antimicrobial agent with a molecular weight of about 200 to about 700, an inorganic property/organic property value of about 0.3 to about 1.4 and an average particle size of about 2 xcexcm or less and, preferably, treating simultaneously with dyeing under pressurization.
As another embodiment, the antimicrobial article can also be obtained by applying a liquid containing the same pyridine based antimicrobial agent to a fibrous product by padding or spraying, and heat-treating at about 160 to 200xc2x0 C. in a dry or wet state.
It will be appreciated that the following description is intended to refer to specific embodiments of the invention selected for illustration and is not intended to define or limit the invention, other than in the appended claims.
A preferable antimicrobial agent used in the present invention has a molecular weight of about 200 to about 700, an inorganic property/organic property value of about 0.3 to about 1.4 and an average particle size of about 2 xcexcm or less.
A pyridine based antimicrobial agent is stably infiltrated and diffused into a molded article, especially synthetic fibers and synthetic resin films. The molded article can also be of any other form such as a film, sheet, plate or rod. However, for the sake of simplicity, this description is limited to cases of fibers. We have discovered that the antimicrobial agent dispersed in the molded article shows behavior similar to that of the disperse dye if the antimicrobial agent is particularly selected to be closer to the disperse dye in three requirements: molecular weight, inorganic property/organic property value and average particle size.
However, it is surprising that the solid antimicrobial agent forms independent phase of about 0.01 xcexcm or more in xe2x80x9cshort diameterxe2x80x9d inside the fibers, and that about 50% or more of the antimicrobial agent is infiltrated to a depth range of about 0.5, preferably, about 1 xcexcm or more from the surfaces of the fibers or that about 30% or more of it is infiltrated to a depth range of about 2 xcexcm or more from the surfaces of the fibers. xe2x80x9cShort diameterxe2x80x9d as used herein means the number average diameter of independent phases taken through a cross section of the fiber.
It is not clearly understood that the antimicrobial agent can be diffused as particles in the highly crystalline and structurally dense fibers. However, without being bound by any particular theory, we believe that the antimicrobial agent is dispersed as, respectively, single molecules or groups consisting of several cohesive molecules, to be precipitated which forms independent phases of agent in the particles in the fibers. As for the diffusion degree of the antimicrobial agent, if the distance from the fiber surface to the center of the fiber section is set at 1, the antimicrobial agent is infiltrated and diffused into the fiber at least a distance of about 0.2. As for the concentration distribution of the antimicrobial agent, the ratio of the concentration of the antimicrobial agent existing in a range from the center of the fiber section to a distance nearest to the center of the fiber section to the concentration of the antimicrobial agent existing in a range from the center of the fiber section to the surface is about 1:1 to about 1:10. Thus, the antimicrobial agent is sufficiently infiltrated inside the fibers. Unless these conditions are satisfied, the antimicrobial agent is not properly diffused into the synthetic fibers, and sufficient industrial washing durability cannot be obtained.
Washing durability is low if the molecular weight of the antimicrobial agent is less than about 200, even when the antimicrobial agent is infiltrated and diffused into the synthetic fibers. On the other hand, the antimicrobial agent is not infiltrated into the synthetic fibers if its molecular weight is more than about 700. It is preferable that the molecular weight of the antimicrobial agent is about 300 to about 500.
The xe2x80x9cinorganic property/organic property valuexe2x80x9d referred to in the invention is a value defined by Minoru Fujita for expressing the polarity of various organic materials [Revised Edition, Science of Chemical Experimentsxe2x80x94Organic Chemistryxe2x80x94Kawade Shobo (1971)]. Specifically, it is a ratio of the sum of inorganic property values to the sum of organic property values obtained from the inorganic property values and organic property values of various polar groups shown in Table 1 with the organic property value of one carbon atom as 20.
The inorganic property/organic property value of polyethylene terephthalate calculated according to this method is 0.7. The affinity between synthetic fibers and the antimicrobial agent based on the value calculated according to this method, and an antimicrobial agent with the inorganic property/organic property value kept in the predetermined range is sufficiently infiltrated and diffused in the synthetic fibers.
If the inorganic property/organic property value is less than about 0.3, the organic property is too strong, and if more than about 1.4, the inorganic property is so strong that the antimicrobial agent is less likely to be infiltrated and diffused into the synthetic fibers. It is preferable that the inorganic property/organic property value is in a range of about 0.35 to about 1.3, more preferably from about 0.4 to about 1.2.
For example, 2,3,5,6-tetrachloro-4-hydroxypyridine has an inorganic property value of 265 since it has one benzene nucleus, fourxe2x80x94Cl groups, onexe2x80x94OH group and onexe2x80x94NR group, and has an organic property value of 180 since it has five carbon atoms and fourxe2x80x94Cl groups. Hence the inorganic property/organic property value of the compound is 1.47. Furthermore, 2-pyridylthiol-1-oxide zinc exists as a chelate complex, and judging from its electronegativity, it is considered that zinc and sulfur form a covalent bond. Thus, the compound has an inorganic property value of 85 and an organic property value of 190 and, hence, an inorganic property/organic property value of 0.45, according to the calculation method.
On the other hand, in the case of 2-pyridylthiol-1-oxide sodium, which is also a pyridine based antimicrobial agent, since the electronegativity difference between sodium and sulphur is more than 1.6, the bond is an ionic bond. In this case, sodium acts as a light metal salt. Thus, the compound has an inorganic property value of 585 and an organic property value of 190 and, hence, an inorganic property/organic property value of 3.0, according to the calculation method. It is poor in affinity to polyesters.
It is preferable that the antimicrobial agent has an average particle size of about 2 xcexcm or less. The antimicrobial agent is less likely to be infiltrated and diffused into the synthetic fibers if the average particle size is more than about 2 xcexcm, and when the antimicrobial agent is provided as an aqueous liquid, the particles precipitate. Hence, the liquid tends to be poor in stability. It is preferable that the average particle size of the antimicrobial agent is about 1 xcexcm or less.
The antimicrobial agents which can be used in the invention include, but are not limited to, pyridine based compounds such as 2-chloro-6-trichloromethylpyridine, 2-chloro-4-trichloromethyl-6-methoxypyridine, 2-chloro-4-trichloromethyl-6-(2-furylmethoxy)pyridine, di(4-chlorophenyl)pyridylmethanol, 2,3,5-trichloro-4-(n-propylsulfonyl)pyridine, 2-pyridylthiol-1-oxide zinc, and di(2-pyridylthiol-1-oxide). Among them, 2-pyridylthiol-1-oxide zinc is especially good in affinity to fibers, and is stably filtrated into the fibers. It has good washing durability and is also preferable in view of the variety of microbial strains including MRSA against which it is effective.
The materials of the synthetic fibers which can be used as the fibrous product of the invention can be polyesters, acrylic resins, nylons and the like. The fibrous product of the invention can also be natural fibers of cotton, wool or silk and the like, in addition to those synthetic fibers, or a combination with semi-synthetic fibers such as rayon, as yarns, woven fabric or nonwoven fabric and the like. Among such synthetic fibers, polyester fibers can provide a fibrous product most excellent in industrial washing durability of antimicrobial activity.
Furthermore, in the invention, the fibers can be colored. In other words, the fibers may contain a colorant such as disperse dye, acid dye, cationic dye or fluorescent whitening agent.
In considering antimicrobial activity, depositing the antimicrobial agent on the surfaces of fibers is most preferred since the frequency of contact with bacteria is high. However, in this state, the antimicrobial agent is likely to be removed and, accordingly, washing durability is not good. On the other hand, if the antimicrobial agent is diffused into the fibers and forms independent phases within the particles of about 0.01 xcexcm or more in short diameter inside the fibers, washing durability is high, although the antimicrobial activity is not as high.
With regard to washing durability, it is preferable that the size of the antimicrobial agent in the fibers is about 0.02 xcexcm or more in short diameter. Although a larger size such as about 0.5 xcexcm or about 1 xcexcm can be effective, the size of the independent phases is preferably about 0.02 to about 0.5 xcexcm in short diameter. Typically, it is about 0.02 to about 0.2 xcexcm. For these reasons, it can be considered to be excellent in view of both antimicrobial activity and washing durability that the antimicrobial agent is distributed substantially annularly near the surface of each fiber inside the fiber, or diffused like branches from the surface of each fiber into the inside, or distributed as xe2x80x9clumpsxe2x80x9d inside each fiber. This distribution may be random, uniform or otherwise.
The concentration distribution of the antimicrobial agent inside each fiber can be easily confirmed by analyzing a section of the fiber using an X-ray microanalyzer (EMAX-2000 produced by Horiba Seisakusho), and evaluating the concentration distribution of any specific element such as sulfur contained in the antimicrobial agent inside the fiber.
The state where the antimicrobial agent forms independent phases of about 0.01 xcexcm or more in short diameter inside each fiber, the state where it is distributed substantially annularly near the surface of each fiber, the state where it is diffused like branches from the surface to inside of each fiber inside the fiber, or the state where it is distributed as lumps inside each fiber can be confirmed by observation with a scanning electron microscope (SEM).
The concentration distribution of the antimicrobial agent inside each fiber can be controlled into several states by changing the processing conditions into the state where the microbial agent is deposited on the surface of each fiber, into the state where it is distributed substantially annularly in a range from the surface to the inside of each fiber, into the state where it is diffused like branches inside each fiber, or into the state where it is distributed as lumps inside each fiber.
It is also preferable that the microbiostatic activity value measured according to the microbe control evaluation method (standard testing method) specified by SEK (Seni Seihin Shin-kinou Hyouka Kyougikai: New Function Evaluation Conference for Fiber Goods) is about 2.2 or more after 50 times of industrial washing treatment for 12 minutes/wash at 80xc2x0 C. using a washing liquid containing a surfactant. It is more preferable that the same microbiostatic activity value is maintained even when the washing time is changed to 15 minutes/wash.
It is further preferable that the microbiostatic activity value is about 2.2 or more even if the washing treatment conditions are more severe. That is, it is further preferable that the same microbiostatic activity value is maintained even when a washing liquid containing a peroxide, strong alkali and surfactant was used. It is most preferable that the same microbiostatic activity value is maintained even when the washing time was changed to 15 minutes/wash and the washing liquid containing a peroxide, strong alkali and surfactant was used.
The washing liquid containing a peroxide, strong alkali and surfactant in this case is prepared, for example, by supplying 2 g/l of detergent xe2x80x9cZabxe2x80x9d produced by Kao Corp., 3 cc/l of hydrogen peroxide water (35% industrial use) as a peroxide, and 1.5 g/l of sodium percarbonate as a strong alkali into a drum dyeing machine filled with water at a bath ratio of 1:20, and mixing them. The washing liquid is heated to 85xc2x0 C., and an antimicrobial fibrous product of the invention and waste cloth are supplied into the liquid, for washing for 15 minutes. The machine is then drained, and the fibrous product is dewatered, washed by water with overflowing for 10 minutes, and finally dewatered. This washing is repeated 50 times, and the fibrous product is dried by a tumbler dryer for 20 minutes, for microbe control evaluation.
The process for producing the antimicrobial fibrous product of the invention is described below.
At first, a fibrous product is immersed in a liquid containing any of the pyridine based antimicrobial agents and a colorant such as a disperse dye, acid dye, cationic dye or fluorescent whitening agent in a jet dyeing machine, and heat-treated at atmospheric pressure or under pressurization at about 90 to about 160xc2x0 C. It is preferable that the heat treatment time is about 10 to about 120 minutes. It is more preferable to heat-treat at about 120 to about 135xc2x0 C. for about 20 to about 60 minutes. In this case, since the colorant and the pyridine based antimicrobial agent are heat-treated simultaneously in the liquid, the antimicrobial agent is deposited on the fibers and infiltrated and diffused inside the fibers like the dye. If the pyridine based antimicrobial agent is heat-treated in a bath at about 90 to about 160xc2x0 C. after the fibrous product has been dyed, the colorant is desorbed from the fibers, not allowing the desired coloring to be achieved. On the other hand, if the fibers containing an antimicrobial agent are colored, the pyridine based antimicrobial agent is desorbed to lower the microbe control performance. If the heat treatment is effected at lower than about 90xc2x0 C., the antimicrobial agent is not infiltrated in the synthetic fibers. If higher than about 160xc2x0 C., the effect obtained is not high enough to be proportional to the energy consumption, thus lowering cost performance.
It is preferable that the fibrous product treated in the liquid according to the above method is treated by dry heat of about 160 to about 200xc2x0 C., using a tenter dryer or the like. The treatment time can be about 15 seconds to about 5 minutes. It is more preferable that the dry heat treatment is effected at about 170 to about 190xc2x0 C. for about 30 seconds to about 2 minutes. The dry heat treatment causes the antimicrobial agent to be diffused inside from the surfaces of the fibers, being distributed substantially annularly inside the fibers, or infiltrated and diffused like chains, to improve the washing durability without impairing the antimicrobial activity. If the heat treatment is effected at lower than about 160xc2x0 C., the effect of dry heat treatment is less likely to be obtained. If higher than about 200xc2x0 C., the fiber material is yellowed or becomes fragile, and the dye and the antimicrobial agent are sublimated or thermally decomposed while energy consumption increases. The respective states of adhesion of the antimicrobial agent can be controlled by changing the treatment conditions into being deposited on the surfaces of fibers, into substantially annular distribution inside the fibers or into diffusion inside the fibers.
As another embodiment of the process for producing the antimicrobial fibrous product of the invention, a liquid containing any of the pyridine based antimicrobial agents is applied to a colored fibrous product by padding or spraying, and the fibrous product is heat-treated in dry or wet state at about 160 to about 200xc2x0 C. It is preferable that the heat treatment time is about 30 seconds to about 10 minutes. It is more preferable that the heat treatment is effected in a dry or wet state at about 170 to about 190xc2x0 C. for about 2 to about 5 minutes. If the heat treatment temperature is lower than about 160xc2x0 C., the pyridine based antimicrobial agent is not infiltrated in the fibers. If higher than about 200xc2x0 C., the fiber material is yellowed or becomes fragile and the dye and the antimicrobial agent are sublimated or thermally decomposed while the energy consumption increases.
It is preferable that the pyridine based antimicrobial agent is granulated in a colloidal state. If the antimicrobial agent is colloidal, it can be stably infiltrated and diffused in the fibers. Especially if it is made colloidal by water and a formalin condensation product, the antimicrobial agent becomes higher in dispersibility and can keep a good dispersed state, being good in affinity to the synthetic fibers.